What does 'reduced pressure' refer to in the context of gas measurement?

The term 'reduced pressure' specifically refers to the pressure of a gas measured relative to a vacuum, which is considered a perfect lack of pressure. When we mention reduced pressure in gas measurements, we often mean the pressure that has been adjusted or referenced against absolute zero pressure, reflecting how much pressure is present above a complete vacuum.

In practical applications, this concept is crucial for processes that occur in environments where absolute pressure is significantly less than atmospheric pressure, such as in vacuum systems.

The concept differs from atmospheric pressure, which is the pressure relative to the standard atmospheric conditions, and absolute pressure, which measures the total pressure including atmospheric influence. Furthermore, STP conditions denote specific temperature and pressure standards (0°C and 1 atm), which do not directly correlate with the concept of reduced pressure. Thus, reduced pressure is best described as the pressure of a gas relative to a vacuum, highlighting the absence of pressure in a sealed environment.